The boarding of U 110 in may 1941 and subsequent seizure of documents, is well known, but until recently I was uncertain as to their value. But I recently found buried in an NID file, the story of the attempt by British intelligence in the first half of 1941 to reconstruct the German grid map for the Atlantic. Not surprisingly this was proving difficult, even with the breaking of the Enigma codes in the spring of 1941. The file also documents that the most important thing taken from U 110 was the complete grid map for U boats for the Arctic, and the North and Central Atlantic. This , coupled with the major break into German enigma completed most of the picture for U boat operations. If this piece of information (re - the grid map) is already well known, I apologise for posting it here.